Rheostat and potentiometer



May 12, 1936. D. T. SIEGEL mmosmw AND POTENTIOMETER Filed Dec. 21, 1933 llffi'rz'ez'sed: jni/erzi'or" W W 1701/14 7 J'zgel Patented May I RHEOSTAT POTENTIOMETEB nma nsiml; Chicago, 111. j Application Deeember 21, 193:, Serial 'No. 703,401

I I 4 mm. (0L sol-w This invention relates to means for attaining bemounted. As the turnis tightly drawn around alined contact surfaces on the resistance elethe core it binds the clip in position against the ments of rheostats and similar instruments core. These clips are shown as all lying in the whereby substantially uniform contact be same plane on the top of the core and may there brought about between each of said contact surfore be conveniently ground sov that their-surfaces 5 faces and a brush which is adjustable from conare trued to the same plane, but before the grindtact to-contactto bring more or less of the reing operation the clips arepermanently united to I sistance wire into the brush circuit. the wire, and the ends of the winding are welded The objects of the invention are attained by to terminal clips-4 and 5, and an insulating enmans of a method of forming resistance units amel i. is applied and baited to the unitfor the 10 and a construction as herein illustrated .andde purpose of embedding and retaining each con- Scrlbed n the rawin volution against displacement and cementing the Figure 1 is a plan view ofthe rear face of the. core to the base I. By the term permanently instrument. 1 united I intend to cover welding, brazing, or

,15 Fig. 2 is a plan view of the insulating core for soldering; that is, union by fusion of metals as the coil and shows the coil thereon in the process distinguished from mere contact by clamping two of winding and applying the clips; parts together. In order to insure a good elec- Fi'g. 3 is a sectional view as indicated by the trical contact it. is desirable that one or both of line 3-3 on Fig. 1. the leaves of the clip should be completely joined 20. Fig. 1 is a perspective view of one of the conto the ribbon before the enamel in fluid form is t clips. applied; otherwise the insulating enamel is like- Fig. 5' is a sectional detail of the wound core, ly to flow between the parts and when the bakshowing a brush bearing against one of the 'coning takes place, actually break what might othertac't clips. wise be a fairly good contact.

In the forming of wound resistance unit s, par- In Fig. 1 the finished unit is illustrated and 25 tic'ularly such units as are made by winding a includes a central terminal element 8 which is I resistance wire around a molded insulating core; electrically connected with brush 8 carried upon irregularities in the surface of the windingmay the rotatably mounted arm II and held thereby occur because of imperfections in the core or. resiliently against the contacting surfaces of the the mounting thereof or manner of cementing clip. A

the winding to the core, 'or seating and securing The brush carrying arm I0 is bent upon itself the resistance (element to a base. This uncer-- as indicated vat II, and terminates in a ring tainty regarding the uniformity of the contactshaped contact I! which encircles the hub of an ing portions of the winding is overcome by means insulator II and contacts with the stationary of the present invention which consists in clipcentral terminal element]. v 35 I ping to separate .convolutions of the sep- The brush has recess 14 for receiving the bent arate contact elements which are welded to the I end of its operating arm II, and the latter is wire in aligned position along the element. notched out at ll toreceive lugs It on the in- I Theexposed surfaces of the clips are then sulator' l3.- Thus the brush arm is rotated by 40 I trued up by a grinding operation. It is then posturning the insulator and the insulator is pinned 4 sible to bring about uniformly good connections to shaft II, which carries the operating knob l8. betweena brush which is movable along the coil The .clips 8 are applied to the separate turns and the separate contacting elements of the of the resistance wire preferably as the wire is 11, e l wound upon the core, and the clips are tightly I the illustration ainolded'horseshoeshaped bound the surface n of the insulating .45

insulating core I haswound thereon a flat resist-' core by the wire. .Whenvthe winding is comance wire or=ribbon 1. As the winding proceeds, pleted the end terminals 4 and 5 are clipped over metallic clips 3 are regularlyapplied to separate the ends of the core in contact. with the ends turns of the winding as illustrated in ,Fig. 2. of the wire. and then the unit is welded, so as 50 These clips," as best' shown in Fig.4, are each 'to weld each clip I to its particular convolution of formed from a rectangular section of sheet metal, the wire and to weld the terminals. 4 and Ho the doubled on itself to provide a very narrow space endsofthe wire. The wound core is then placed between leaves; that is, a space not mainthe receiving recess 2. of the insulating base terially greater in depth .than the thickness of 1 and the article is dipped inan insulating enamel 66 the ilat wire or ribbon on which the clip is to which serves'to permanently bind all parts in 5.5

their set positions. The enamel is removed. preferably after hardening, from the outer surfaces of the clips 3. Then the exposed surfaces of the clips are ground to render them absolutely flat and true to the same plane. By this last operation correction is made for irregularities which otherwise might occur due to imperfections of the core or lack of uniform tension in the separate convolutions oi the coil. The enamel will fill the spaces between the elevated portions formed by the clips. but after baking will be slightly below the clip surface.

If the brush were to ride over the surface of the coil rather than on the finished surfaces of the clips, a uniform area of contact .between the brush and segments of the coil in the various settings of the brush could not be maintained as well as with the trued-up surface provided for by the clips. In using the instrument electric connections are made with the terminals 4, 8, and 5, according to whether it is used as a rheostat or potentiometer, and the desired amount of resistance wire is brought into the circuit by the usual adjustment of the brush carrying arm through rotation of the operating knob 18. The contact clips perform the function not only of improving the contact surface but also of reducing the resistance, and consequently the heat, at the contact surfaces. Inasmuch as rheostats of the type shown herein are intended for high duty-that is, the handling of heavy wattagethe heat developed is usually very high. Consequently the reduction of such heat on the actual contact area is desirable.

Although but one specific embodiment of this invention is herein described, it will be understood that details of the construction shown may be altered or omitted without departing from the spirit of this invention as defined by the following claims.

I' claim:

1. A rheostat comprising an insulating core having wound thereon a hat ribbon resistance element, and flat U-shaped contact clips app1ied to separate turns of the resistance element.

2. A rheostat comprising an insulating core having wound thereon a flat ribbon resistance element, and flat U-shaped sheet metal contact clips applied to separate turns of the resistance element.

3. The method of making a high duty rheostat which consists in forming clips by doubling a section of metal on itself, winding a flat resistance wire on a core and progressively applying said clips to the wire during winding whereby the clips are clamped against the core with a portion 01' each clip projecting above the wire surface, then permanently uniting the clips and wire, then embedding the wire and clips in a vitreous enamel and baking the enamel, and then truing the brush contact area.

4. A rheostat comprising in combination a core and base composed of heat resisting dielectric material, a flat resistance wire wound on the core, contact clips each composed of a section of metal doubled on itself and applied to the wire,

one leaf of the clip being clamped between the :2

wire and the core and the other leaf projecting above the surface of the wire, and vitreous enamel covering the winding joining the core to the base and embedding the clip, and a contact brush engaging the elevated portions of the clips.

DAVID T. SIEGEL. 

